Low loss ridged microstrip line for monolithic microwave integrated circuit (MMIC) applications

Abstract

A microstrip line device is disclosed of the type which typically includes a strip conductor disposed on the top of a substrate. The device further includes a layer of dielectric material disposed between the strip conductor and the substrate for reducing the dissipation loss in these devices. In order to accomplish this, the dielectric layer has a dielectric constant which is less than the dielectric constant of the substrate.

What is claimed is: 
     
       1. A microstrip line device of the type including a strip conductor of a first width, disposed on the top of a substrate, wherein the improvement therewith comprises: a layer of dielectric material of a second width, disposed between said strip conductor and said substrate, wherein said substrate contacts said dielectric layer across said second width, and said dielectric layer has a dielectric constant which is less than the dielectric constant of said substrate, wherein said second width of said dielectric layer is no greater than the first width of said strip conductor.   
     
     
       2. The device of claim 1, wherein said dielectric layer is a layer of polyimide material. 
     
     
       3. The device of claim 2, wherein said polyimide layer has a thickness in the range of 5 to 15 um. 
     
     
       4. The device of claim 2, wherein said polyimide layer has a thickness of 7 um. 
     
     
       5. The device of claim 1, wherein said dielectric layer has a dielectric constant of 3.0 and said substrate has a dielectric constant of 12.9. 
     
     
       6. The device of claim 1, wherein said substrate is a Gallium Arsenide (GaAs) material. 
     
     
       7. The device of claim 1, wherein said substrate has a thickness of 75 um. 
     
     
       8. The device of claim 1, wherein said strip conductor has a thickness of about 4.5 um. 
     
     
       9. The device of claim 1, which further includes a ground plane disposed on a lower surface of said substrate. 
     
     
       10. A microstrip line device, comprising: a substrate;   a strip conductor of a first width; and   a layer of dielectric material of a second width, disposed between said strip conductor and said substrate, wherein said substrate contacts said dielectric layer across said second width, and said dielectric layer has a dielectric constant which is less than the dielectric constant of said substrate, wherein said second width of said dielectric layer is no greater than the first width of said strip conductor.   
     
     
       11. The device of claim 10, which further includes a ground plane disposed on a lower surface of said substrate. 
     
     
       12. The device of claim 10, wherein said dielectric layer is a layer of polyimide material. 
     
     
       13. The device of claim 12, wherein said polyimide layer has a thickness in the range of 5 to 15 um. 
     
     
       14. The device of claim 12, wherein said polyimide layer has a thickness of 7 um. 
     
     
       15. The device of claim 10, wherein said substrate is a Gallium Arsenide (GaAs) material. 
     
     
       16. A method for reducing the dissipation loss of a microstrip line including a strip conductor of a first width, disposed on the top of a substrate, said method comprising the steps of: inserting a layer of dielectric material of a second width, between said strip conductor and said substrate, wherein said substrate contacts said dielectric layer across said second width, and said dielectric layer has a dielectric constant which is less than the dielectric constant of said substrate, and   etching said dielectric layer to reduce said second width of said dielectric layer to a width no greater than the first width of said strip conductor.   
     
     
       17. The method of claim 16, wherein said dielectric layer is a layer of polyimide material.